Sound of potentiometer materials?

[FIX]

With an EQ, the only circuit that seems susceptible to amplify pot noise is the active Twin T circuit as it is an open loop circuit with a lot of gain. (GML, Sonnet, ITI, Tonelux), most others are forgiving.

Carbon pots will add a pleasant 2nd harmonic content, as carbon tends to do that. Because carbon is kind of rough, it wears the wiper faster, and if you DC offset, it will be the noisiest. In fact, any legit pot manufacturer will specify the polarity for the lowest noise and oxidation.

Conductive plastic is pretty quiet, But only a few make them. ALPs, Bourns (because I told them about it) and a few others use whats called polished carbon, which works as well as conductive plastic, as it's also shiny and tends not to wear much.

None of the above have ever caused a song to be or not to be a hit.

 

[Newmarket]

Is there data that supports this? In practice I've have cermet pots wear our quicker with repeated use. But they were also in different mechanical packages so hard to conclude for sure the failure mechanism.

I avoid cermet unless it's a minimal use set and forget type application.

I don't have data. But Cermet is "harder" so there's logically a compromise between a "hard" wiper that has a longer life but is "scratchy" and "softer'" wiper that wears more quickly but is less scratchy.
For context, I am an ex-employee of Penny&Giles. Afaik at no point did anyone suggest manufacturing cermet pots or faders for audio applications.
And no one talked about the "tonality" of CP. All about reliability, multi-finger wipers, lubrication, feel, taper etc...

 

[Brian Roth]

BI Technologies / TT Electronics also makes CP pots. Mouser stocks various versions, and I've had good luck with some of the rotary models. They also sell slide pots, but I don't know if those have carbon or CP elements.

Bri

 

[soapfoot]

I used to have great discussions with an old friend (now RIP) who was also a console designer, about ergonomics or "human factors". Customers have difficultly discriminating between things like audio path linearity, and control laws (gain, or boost/cut), and control feel...

...

In my experience customers buy almost as much on how faders feel than what they sound like. Subtle things like control laws can dramatically affect user perception. An EQ that is too fast or too slow can make a bad impression.

As much as most of us would be loath to admit it, the same is true even with musical instruments. Having learned a bit about my own cognitive biases over the years, I'm positive I've conflated "the lacquer on the neck has been worn to feel really pleasant and smooth" with "this old guitar really sounds amazing and has something that the modern guitars can't get."

Plus a million other small things like that...

 

[abbey road d enfer]

I don't have data. But Cermet is "harder" so there's logically a compromise between a "hard" wiper that has a longer life but is "scratchy" and "softer'" wiper that wears more quickly but is less scratchy.
For context, I am an ex-employee of Penny&Giles. Afaik at no point did anyone suggest manufacturing cermet pots or faders for audio applications.

I have used extensively cermet pots, just because of a business relationship with a french manufacturer (now extinct). In order to fix the scratchiness issue, he used carbon wipers, which were supposed to have reduced durability. Actually, many units are still in use and there is no undue scratchiness or other issue.

 

[Newmarket]

I have used extensively cermet pots, just because of a business relationship with a french manufacturer (now extinct). In order to fix the scratchiness issue, he used carbon wipers, which were supposed to have reduced durability. Actually, many units are still in use and there is no undue scratchiness or other issue.

Out of curiosity - what are those products ?

 

[abbey road d enfer]

Out of curiosity - what are those products ?

SCV Electronics, which became LA Audio when mfg went to the UK.

 

[Newmarket]

SCV Electronics, which became LA Audio when mfg went to the UK.

Thanks.

 

[JohnRoberts]

I have used extensively cermet pots, just because of a business relationship with a french manufacturer (now extinct). In order to fix the scratchiness issue, he used carbon wipers, which were supposed to have reduced durability. Actually, many units are still in use and there is no undue scratchiness or other issue.

I am having a little difficulty visualizing carbon pot wipers. Would that be similar to brushes inside electrical motors?

JR

 

[abbey road d enfer]

I am having a little difficulty visualizing carbon pot wipers. Would that be similar to brushes inside electrical motors?

JR

Yes. It was a little round piece of carbon crimped in a thin metal finger.

 

[Newmarket]

Carbon pots will add a pleasant 2nd harmonic content, as carbon tends to do that. Because carbon is kind of rough, it wears the wiper faster, and if you DC offset, it will be the noisiest. In fact, any legit pot manufacturer will specify the polarity for the lowest noise and oxidation.

None of the above have ever caused a song to be or not to be a hit.

Does carbon really do that ? Not aware although tbf I was only involved in working with CP pots / faders.
Any figures / results as to the magnitude of the harmonic(s).

Yes !

 

[Tubetec]

Ive seen pots with carbon wipers going back long ago , Morganite used it , they were renowned for very long life and good 'feel' .

Good guitar pots are hard to find , getting a pleasing sweep across the turn range doesnt happen with the usual cheap Chinese pots , CTS seem to be the best at making these , the peculiarities of impedences involved with guitar pickups and and amp inputs mean a special 'law' is used ,
your standard off the shelf volume control doesnt work well for guys who adjust volume a lot as part of the dynamics of the performance . Proper balance between volume and tone is another important factor .

Might be interesting to plot the curve of a few modern pots and compare with vintage samples and modern known good samples .

As far as the materials resistors are made from , it does appear to matter if your looking down at macro level , Ivan of E1DA reports a difference in the proportions of harmonic distortion levels in his testing of the Cosmos APU depending on the brand used , he got stung with some counterfit Viking Melf resistors which he tried and they indeed wernt as good as the real thing , having said that what proportion of this distortion is caused by the materials themselves or the resistance tollerances (accumulated) ,who knows maybe he went to the trouble cold testing and matching the resistors off the roll , either way Ivan was off to source even closer tollerance parts to try and trim out even better performance ,
He has a Cosmos topic , I think on Diyaudio, he only updates it once in a while with important stuff , well away from the the shitstorm of dickheads he has to deal with on Dischord .

Coffee time here ,

 

[abbey road d enfer]

Carbon pots will add a pleasant 2nd harmonic content, as carbon tends to do that.

That is a quite interesting claim.
Indeed, carbon resistivity changes with the electric field, as it tends to orientate the molecules, but this is an isotropic effect, meaning it has the same effect whatever the polarity. As a consequence, the effect on signal is mainly 3rd-order distortion.
No study of resistor voltage coefficient shows an asymetric behaviour. Actually they all show the presence of 3rd-order.
However, potentiometers have a significant difference with resistors; where resistors have two symmetrical metal-carbone junctions at the ends of the track, which preserves symmetry, a potentiometer has an additional junction at the wiper. Could it be that this junction has enough rectifying properties to produce this 2nd harmonic? Then distortion would depend on the wiper position, with a maximum at mid-rotation, and minima at both ends. This is assuming the wiper junction is of identical nature as the end junctions.

 

[Tubetec]

The usual pots now are a thin deposited layer of carbon on a substrait ,
the way some of the older ones are made is different , theres a very high quality pot used in all the quality UK gear from long ago , I forgot the name now , it consists of a moulded brown phenolic insulator with the three terminals and a circular trough of tapering or stepped depth which is filled with what ever carbon/binder formulation they used , a carbon wiper is used also .

Were into a funny place here where not only is it the sound but how the controls interact with it and it feeds back to our brain . Ok on studio gear your controls are labeled in db , but in a guitar amp , 1-10 , the scale is utterly meaningless ,its merely a reference point for our brains to interact with the thing in the future .

 

[Brian Roth]

Are we saying the choice of potentiometer track material causes a significant change of the sound of the audio passing through it??? That smacks of audiophoolery to me.

Paul made a statement in message #21 in this thread (scroll back):

"None of the above have ever caused a song to be or not to be a hit."

I prefer CP pots for low noise (when adjusting) and long life.


Bri

 

[Newmarket]

Are we saying the choice of potentiometer track material causes a significant change of the sound of the audio passing through it??? That smacks of audiophoolery to me.

Paul made a statement in message #21 in this thread (scroll back):

"None of the above have ever caused a song to be or not to be a hit."

I prefer CP pots for low noise (when adjusting) and long life.


Bri

Apart from the OP I don't think it's being claimed that any change is "significant".
I stand to be corrected !

 

[Brian Roth]

I am probably deaf any more at my age, but I am suspicious when someone claims that a Switchcraft A3M or A3F connector sounds "better" than a similar Neutrik connector (or vice versa). Or, that solid core wire "sounds better" than stranded.

Bri

 

[Brian Roth]

Extraordinary claims require extraordinary proof. Not opinions.

Bri

 

[Brian Roth]

I will state that decent wire from Belden, Mogami, etc MIGHT "sound better" than rusty barbed wire wrapped in duct tape. <g>

Bri

 

[Brian Roth]

John Roberts and I are on the same page re. null testing. Can anyone find a long length pair of rusty barbed wire, wrap it in duct tape, and null test it with a similar length of Mogami/whatever cable??

Bri